Re: [PATCH net 1/2] vsock: add half-closed socket details in the implementation notes

Michael S. Tsirkin
2019-10-11T14:22:39Z

On Fri, Oct 11, 2019 at 03:07:57PM +0200, Stefano Garzarella wrote:
> vmci_transport never allowed half-closed socket on the host side.
> Since we want to have the same behaviour across all transports, we
> add a section in the "Implementation notes".
>
> Cc: Jorgen Hansen <jhansen@vmware.com>
> Cc: Adit Ranadive <aditr@vmware.com>
> Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
> ---
> net/vmw_vsock/af_vsock.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
> index 2ab43b2bba31..27df57c2024b 100644
> --- a/net/vmw_vsock/af_vsock.c
> +++ b/net/vmw_vsock/af_vsock.c
> @@ -83,6 +83,10 @@
> * TCP_ESTABLISHED - connected
> * TCP_CLOSING - disconnecting
> * TCP_LISTEN - listening
> + *
> + * - Half-closed socket is supported only on the guest side. recv() on the host
> + * side should return EOF when the guest closes a connection, also if some
> + * data is still in the receive queue.
> */
>
> #include <linux/types.h>

That's a great way to lose data in a way that's hard to debug.

VMCI sockets connect to a hypervisor so there's tight control
of what the hypervisor can do.

But vhost vsocks connect to a fully fledged Linux, so
you can't assume this is safe. And application authors do not read
kernel source.

> --
> 2.21.0